The multi-party line is a time honored voice communication feature that allows users using multiple terminals to participate in a telephone call. It was widely deployed as a public telephone service when cost of telephone equipment and telephone lines was high.
Multi-party lines have been employed in key systems for small businesses, and in hotel or motel guest rooms. The deployment of cordless telephony based on wireless technologies such as Digital Enhanced Cordless Telecommunication (“DECT”) and Communication Technologies 2 (“CT2”) has fueled the continued use of multi-party lines.
With the advancement of Internet technologies, Internet Protocol (“IP”) networks are becoming an important means for voice and data communications. Internet service providers and equipment vendors roll out successful voice communication services and products at a breathtaking pace. Many of these services and products are based on various Voice over IP (“VoIP”) technologies, such as H.323 and Session Initiation Protocol (“SIP”). However, these VoIP technologies, limited by their reliance on endpoint call state management and their lack of a centralized call processing architecture, are inherently unsuitable for supporting multi-party lines. The lack of a centralized call processing architecture is problematic for supporting multi-party calls because the control of each individual telephone call is concentrated at the call's origination and destination, and once the call is established, an additional party has no centralized call processing entity to request that they be joined to the existing telephone call from. Thus, in attempting to join the existing telephone call in such an endpoint state management system, the additional party will only get a busy signal. The following examples are illustrative of various limitations VoIP technologies have with respect to multi-party lines.
In one example, a caller calls a multi-party line by alerting the multiple telephone terminals of the multi-party line. In a non-VoIP environment, when a first terminal answers the call, the centralized call processing center then removes the call alert from the other telephone terminals and establishes the multi-party call. In the case of a VoIP call, when a first terminal of the multi-party line answers the call, since there is no centralized call processing center, there is no feasible method to notify the other telephone terminals of the multi-party line to remove the call alert, thus the multi-party line call cannot be established.
In another example, a first terminal is conducting a conversation over a VoIP call. When a second terminal of the multi-party line desires to join the call, there is no feasible method to allow the second terminal to join the conversation. For example, if the second terminal attempts to call the first terminal, it receives a busy signal. Under systems using a centralized call processing center, the center is able to verify the second terminal as authorized on the multiple-party line call, and allow them to join in the already-initiated call.
In another example, a first user subscribes to a single-line residential telephone service. The first user connects the base station of her old 2.4 GHz multi-handset to the telephone line, with one handset in the kitchen, and the other handset in her daughter's bedroom. With this set up, the first user and her daughter are able to participate in a telephone call using the two handsets. Impressed with the low cost and the promise of convenience and other advanced features, the first user decides to switch to a 2-line residential VoIP telephone service. Bundled with the service are two brand new VoIP telephones. Each VoIP telephone includes an independent VoIP application, allowing the first user and her daughter to make separate telephone calls at the same time. While enjoying the new found convenience, the first user is unaware of the limitation that the multi-party line feature no longer works. While conducting a conversation with second user, such as a relative, over the VoIP telephone in the kitchen, the first user wants her daughter to join the conversation using the VoIP telephone in her room. When the daughter picks up her phone, she is unable to join the conversation, since there is now no centralized call processor. Instead she receives a dial tone, prompting her to make a new call.
In still another example, a user owns a small business and subscribes to a single-line business telephone service. The user uses a telephone connector to connect two telephones to the telephone line. With this set up, the user can monitor the way his employee handles customer calls, and at time can join the conversation when necessary. With the expansion of his business, the user hires two new employees and switches to a 4-line VoIP business telephone service. With the new setup, the user and his employees can simultaneously handle multiple customer calls. However, the user can no longer monitor his employees' performance, and offer his help.
In another example, a hotel has upgraded its guest rooms to use VoIP technology. Each telephone runs a separate VoIP application, and each connects to the hotel's IP-Public Branch Exchange (IP-PBX) to receive telephone service. A user is a frequent patron of the hotel. Before the upgrade, she was able to use any telephone in the guest room to engage in a call. Unaware of the recent upgrade, she checks into the hotel the night before an important strategic presentation to her customers. She checks into an executive suite that features multiple VoIP telephones, one at the night stand in the bedroom, one on a desk in the adjacent living quarter, and one in the bathroom. At two o'clock a.m., the telephone rings. She wakes up and picks up the call with the VoIP telephone at the night stand and speaks to her boss regarding critical changes in the customer presentation. After talking for a minute, she decides to move to the living quarter in order to review the presentation in her laptop while expecting to resume the conversion with her boss with the VoIP telephone at the desk. But when she picks up the VoIP telephone, she is unable to speak to or hear from her boss, because there is no centralized call processor tying the telephone lines in the room together into a multi-party line.
The foregoing examples demonstrate the need to provide multi-party line features over an IP network.